1. Field of the Invention
The present invention relates to a moving picture coding system, and more specifically to a moving picture coding program, a program storage medium, and a coding apparatus for preventing picture degradation after a scene change by decreasing the amount of data used in coding an image immediately before the occurrence of the scene change which is scarcely left in the consciousness of a person when the scene change occurs between two frame images
2. Description of the Related Art
Recently, various standards such as H. 261 for an ISDN moving picture transfer, H. 262 for processing a broadcast medium moving picture, H. 263 for a television telephone by an existing telephone network, MPEG-1 for an storage medium moving picture, MPEG-2 in accordance with substantially the same standard as H. 262, MPEG-4 for general-purpose multimedia for a computer, communications, a broadcast, domestic electric appliances, etc. have been set as moving picture coding systems, a moving picture is coded, and a corresponding moving picture is decoded in various fields.
With these moving pictures, there is normally a small change in image data between, for example, two frame images, and the compression coding of a moving picture can be performed by obtaining, for example, an inter-frame difference. However, when a scene change in which, for example, a portrait is changed to a landscape occurs, it is hard to efficiently apply the time difference coding, for example, an inter-frame difference coding system, and there occurs an increase in the amount of coded data, that is, the amount of generated information, to be transmitted to a decoding side, that is, the decoder side. Since the entire amount of coding of image data is predetermined, the amount of information allocated to the image data after a scene change eventually decreases when there is an increase in the amount of generated information when the scene change occurs, thereby causing the problem of picture degradation after the scene change.
Generally, relating to the visual consciousness of a person, there is a tendency that an image after a scene change remains in the consciousness of a person when the scene change occurs, and the image immediately before the scene change is hardly left in the consciousness of the person. Nevertheless, if a scene change occurs and a relatively and comparatively large amount of information is allocated to an image immediately before a scene change, the amount of generated information corresponding to the image immediately before the scene change which is visually inconspicuous is practically wasteful.
As the related art to prevent the picture degradation due to the occurrence of a scene change, the patent document 1 discloses a technology of processing some frames immediately after the scene change, in which only a part of the screen is processed in an intra-frame coding mode, and the remaining part is processed in an inter-frame coding mode with the inter-frame difference forcibly set to 0.
The patent document 2 discloses the technology of reducing the block noise. If a scene change is detected in a frame, when coding macro blocks in the frame after the detection, data correction that suppresses high frequency components included in coded output is performed, thereby the block noise is reduced.
The patent document 3 discloses a technology of preventing picture degradation. After determination of a scene change, the coding system of the first target image of the forward predictive coding is changed such that the intra-image coding can be easily performed, by changing the coding system selecting process and the selection standard depending on the determination result of a scene change.
The patent document 4 discloses the coding apparatus for performing coding by decreasing the number of bits to be allocated before a predetermined position determined based on the scene change position by the number-of-bits adjustment device, adjusting the allocation of the remaining number of bits after the predetermined position, and changing the image structure based on the scene change position by a coding device.
[Patent Document 1] Japanese Patent Application Publication No. 9-214977                “Video Coding Method and Video Coding Apparatus”        
[Patent Document 2] Japanese Patent Application Publication No. 9-200769                “Motion Compensation Inter-frame Coding System”        
[Patent Document 3] Japanese Patent Application Publication No. 9-214975                “Scene Change Adaptive Moving Picture Coding Method and Apparatus”        
[Patent Document 4] Japanese Patent Application Publication No. 2004-15351                “Coding Apparatus, Method, Program, and Recording Medium”        
Although the above listed related arts aim at preventing the picture degradation when a scene change occurs as the present invention, for example, the patent document 4 has to change the structure of an image in addition to the adjustment in number of bits, and the related arts generally require complicated control, thereby failing in providing a technology of effectively preventing picture degradation under easier control.